1. Field of the Invention
The present invention relates to a light-emitting element capable of converting electrical energy to light to emit light and more particularly to an organic electroluminescent element.
2. Description of the Related Art
Due to its capability of emitting light with a high brightness at a low voltage, an organic electroluminescent (EL) element has been noted as a promising display element and thus has been under active research and development. However, the organic electroluminescent element leaves something to be desired in enhancement of durability and emission efficiency and reduction of required driving voltage and thus has been desired to have further improvement. Organic electroluminescent elements which comprise a compound having specific spirofluorene skeletons connected to each other with carbonyl group to enhance the emission efficiency thereof have been disclosed (see, e.g., International Patent Publication No. 05/054403 pamphlet and International Patent Publication No. 04/093207 pamphlet). However, these proposals leave something to be desired in durability and emission efficiency. When combined with a light-emitting material having a shorter emission wavelength, these proposals leave more to be desired in efficiency and durability. Referring to light-emitting materials, on the other hand, elements containing a phosphorescent material such as tetradentate platinum complex (e.g., phenylpyridine-platinum complex, phenoxypyridine-platinum complex) have been found to attain a high emission efficiency and thus have been noted (see, e.g., International Patent Publication No. 05/042550 pamphlet, International Patent Publication No. 05/042444 pamphlet and International Patent Publication No. 04/108857 pamphlet).